Yarn withdrawal nozzles for open-end rotor spinning arrangements have been known for a long time in various forms.
In connection with open-end rotor spinning arrangements, there exists the general problem that the real yarn twist introduced by the rotation of the spinning rotor does not evenly enter into the yarn being created.
The real yarn twist is applied to the piece of yarn which is located between the yarn withdrawal nozzle and the yarn withdrawal device of the open-end rotor spinning arrangement.
However, the real yarn twist often enters the piece of yarn located upstream of the yarn withdrawal nozzle only very incompletely.
Since too low a yarn twist in the piece of yarn located between the rotor groove and the yarn withdrawal nozzle has extremely negative effects on the spinning stability of an open-end rotor spinning arrangement, yarn withdrawal nozzles, which are provided with a special surface structure, have already been developed in the past. By means of such preferably rough surface structures it is intended to increase the friction between the surface of the yarn withdrawal nozzle and the rotating yarn and, by means of this to apply a so-called false twist to the piece of yarn being created in addition to the real yarn twist.
Since the false twist extends into the piece of yarn located between the rotor groove and the yarn withdrawal nozzle, an appropriate surface structure of the yarn withdrawal nozzle leads to an improvement of spinning stability of such open-end spinning arrangements.
Numerous yarn withdrawal nozzles in very different embodiments are known in regard to their structural design, their materials or their surface structure.
For example, German Patent Publication DE-OS 25 44 721, German Patent Publication DE 33 44 741 A1 or European Patent Publication EP 0 422 615 B1 describe yarn withdrawal nozzles having notch-like depressions in the area of the yarn feed zone.
In accordance with German Patent Publication DE-OS 25 44 721, the yarn withdrawal nozzle is made of an oxide-ceramic material and has a peak-to-valley height of 0.2 to 0.7 mm in the area of the yarn feed funnel. Moreover, notches, which can have different notch opening angles, are arranged in the area of the yarn feed zone.
The yarn withdrawal nozzles described in German Patent Publication DE 33 44 741 A1 have an exchangeable yarn feed funnel, which is drawn from sheet steel and subsequently hardened.
The yarn feed funnel has either notches or protruding beads.
The notches can also be positioned in two ring-shaped arrangements, located one behind the other in the yarn traveling direction.
European Patent Publication EP 0 422 615 B1 relates to a yarn withdrawal nozzle having notches in the area of the yarn feed zone and protrusions in the area of its yarn withdrawal conduit.
The notches are intended to improve the spinning stability of the open-end spinning arrangement, while the protrusions in the yarn withdrawal conduit are used for producing a particularly hairy yarn.
Furthermore, a yarn withdrawal nozzle is known from Swiss Letters Patent 535 294, which has ring-shaped notches in the area of the inlet funnel, as well as notches which are arranged orthogonally in respect to these ring-shaped notches.
In this yarn withdrawal nozzle, the differently arranged notches overlap and constitute a plurality of relatively aggressive abutments for the rotating yarn. This known yarn withdrawal nozzle has not proven itself in actual use and was unable to prevail in the marketplace.
Although, as a rule, it was possible to somewhat increase the spinning stability of the open-end spinning arrangements by means of the above described yarn withdrawal nozzles, known as “notched nozzles” in the trade, the improvement of the spinning stability was achieved, at least in part, at the expense of the yarn quality that could be achieved.
However, in connection with open-end spinning arrangements, yarn withdrawal nozzles have been known for some time, which have a spiral-shaped structure in the area of the yarn feed zone. Examples of such yarn withdrawal nozzles include German Patent Publication DE 37 07 526 A1, German Patent Publication DE 42 24 632 A1 and European Patent Publication EP 0 220 546 A1.
As described in German Patent Publication DE 37 07 526 A1 or European Patent Publication EP 0 220 546 A1, for example, the spiral-shaped structure can be comprised of strip- or bead-like protrusions, which preferably extend over the entire yarn feed zone of the yarn withdrawal nozzle as far as to the start of the yarn withdrawal conduit of the yarn withdrawal nozzle.
A twist-back-up element with beads extending obliquely in respect to the yarn traveling direction is furthermore connected downstream of the yarn withdrawal nozzle in accordance with European Patent Publication EP 0 220 546 A1.
A yarn withdrawal nozzle with a spiral-shaped structure is described in European Patent Publication DE 42 24 632 A1.
There, the yarn withdrawal nozzle has spiral-like extending faces, which are straight in respect to the yarn traveling direction and are arranged, inclined at an angle, for obtaining yarn deflection points.
In the known yarn withdrawal nozzles, known as “spiral nozzles” in the trade, the yarn, while being withdrawn, slides over the raised parts of the spiral-shaped structures, wherein their orientation has been selected to be such that, with an appropriate rotational direction of the yarn, a push component in the direction toward the rotor groove becomes effective on the piece of yarn being created. This push component causes the real yarn twist introduced by means of the spinning rotor to be at least partially prevented from leaving the area between the rotor groove and the yarn withdrawal nozzle.
In contrast with yarn withdrawal nozzles with a smooth surface, with “spiral nozzles” designed in this way it is possible to retain a higher twist in the piece of yarn upstream of the yarn withdrawal nozzle and thereby to reduce the yarn breaks occurring during the spinning process somewhat, wherein the achieved yarn quality is generally quite good.
Although “spiral nozzles” typically provide better yarn values in comparison with the so-called “notched nozzles”, they have the disadvantage that the spinning stability that can be achieved is often not quite satisfactory.
Therefore, attempts have already been made in the past to unite the respective advantages of the “notched nozzles” with the advantages of the “spiral nozzles” in a single structure.
Such a spiral/notched nozzle is described in German Patent Publication DE 197 38 382 A1, for example.
In this known yarn withdrawal nozzle, a spiral-shaped structure for retaining the real yarn twist is arranged in the inlet area, and notches are additionally positioned in the inlet area of the yarn withdrawal conduit.
The yarn withdrawal nozzles in accordance with German Patent Publication DE 197 38 382 A1 have very well proven themselves in actual use, which means that yarns of exceptional quality can be produced by means of them, in particular when spinning cotton, but also polyester/cotton mixtures.
However, as indicated above, these spiral/notched nozzles, are quite elaborate in respect to their production.
A relatively complex and as a whole quite expensive tool is required in the inlet area of the yarn withdrawal nozzles for producing the spiral-shaped structure.
It is disadvantageous in connection with these yarn withdrawal nozzles that the spiral-shaped structure runs out toward the edge of the yarn withdrawal nozzle, which leads to the distance between the yarn formation zone in the groove of the spinning rotor and the spiral-shaped structure for retaining the real yarn twist continuously changing in the course of spinning.